A variety of techniques are utilized to assess the potential oil recovery from existing boreholes, by making measurements in the borehole indicating the characteristics of the surrounding strata. These techniques include sonic, resistivity, radioactivity (neutron), gravimetry and dielectric constant logging, as well as detailed studies of core samples removed in drilling the borehole and flow rate tests. However, these techniques all have shortcomings since they are affected by the fact that the walls of the borehole have been disturbed by drilling so they have undergone changes such as in internal pressures, and are caked by drilling mud, all of which can lead to inaccurate assessments. Techniques which enabled the measurement of formation characteristics by probes brought to the formation by way of a borehole, while minimizing the effects on the measurements of localized changes caused by the drilling of the borehole, would enable the making of more accurate geological assessments.